In many applications, fasteners provide an efficient means for mechanically joining two parts together. Some fasteners can be of the self-locking type. Self-locking functionality may be achieved by using a special coating patch that is adhered to all or a portion of the fastener surface. The fastener may include other coatings to control torque tension behavior or to provide consistent clamping force at a specific force. The coating may be present as a masking element to prevent damage or contamination fouling to the fastener prior to application of a nut. Such contamination may occur during certain coating and painting processes. Such coatings may also provide anti-seizing functions. In other cases, a coating may be applied to enhance sealing between the mechanical fastener and the aperture in which it is inserted to prevent intrusion of fluids, gasses or particulate matter in a cavity or to retain fluids or gasses within the cavity.
Functional coatings may be present on plugs to provide locking, lubrication, anti-seizing, masking or sealing. In certain instances, the locking function can be minimized to permit removal of the fastener or plug without special tools or treatment such as heating so as to prevent destruction of the fastener or plug or the associated aperture. In such situations, compositions with a low (e.g. less than 75 in. lbs.) or medium (e.g. 75-150 in. lbs.) breakaway torque is suitable, for example, on an M10 fastener or plug.
In some applications, the coating on the fastener or plug can perform more than one of the functions mentioned above imparted by a single coating composition. While some coating compositions may perform in a manner that provides locking and some fluid resistance functions, such composition's dual functionality or multiple functionality is possible only in very limited applications. In a large number of applications, the composition is limited to single functionality. To provide a fastener or plug with multiple functionalities, the part typically is separately coated multiple times, in multiple steps with multiple compositions. Accordingly, there remains room for improvement to provide a single coating for a fastener or plug that can serve multiple functions, and/or to provide a coating composition that provides enhanced single function properties where desired.